About a month ago PICA, the Portland Institute for Contemporary Art, asked us to help with a special art exhibit and workshop by growing indigo. Indigo is an ancient natural dye plant used to dye fabrics all around the world.

Two weeks ago we sowed persicaria tinctoria or polygonum tinctoria seed in seed trays. There are a few types of indigo but we sowed the Japanese or Chinese variety commonly known as dyer's knotweed, a member of the buckwheat family.

The Japanese refer to this plant as "ai". It has been used as a dye since at least 700 bc but was replaced by another type of indigo called indigofera or true indigo. True indigo is in the bean family and is used all around the world to dye blue jeans. This type of can also improve your soil by fixing nitrogen.

Ideally we would have sown the seed after the first frost of the year (usually in April) but because we were contacted only a bit ago we decided to give it our best shot and sow it now. The plant does not tolerate frost so we will be growing it in a hoop house or plastic high tunnel through the winter.

The leaves will be harvested in time for PICA's spring workshop. When a bruise on the leaf leaves a deep blue mark you know it's time to harvest the leaves for dyeing. This means the indican has formed in the plant. The indican is a clear, water-soluble glucoside derived from tryptophan (yup, the same stuff in your turkey meat) that, once oxidized, turns a deep blue. Each leaf contains indican as less than 1% of its volume. Many leaves will go toward making the dye lot they will eventually use.

We're not sure which method PICA will use to dye the fabrics come spring but there are a couple of methods, both of which have fallen out of favor commercially due to the introduction of synthetic indigo and, more recently, crystalline freeze-dried indigo.

The traditional Japanese method, called sukomo, consists of mixing the dried leaves with water and leaving the liquid to ferment for 100 days. This process can be used indefinitely: more ingredients can be added as needed, and the vat of dye can therefore be replenished and used for long periods of time. There are vats out there dyeing fabric today that were started over a 100 years ago!

Another traditional method for producing a dye lot in much shorter order is to boil fresh leaves in a pot of water, add an alkaline substance like baking soda, and introduce oxygen to the liquid by pouring the liquid back and forth between pots, allowing it to aerate with each pass. Indigo dye can be ready to use in as little as day with this method.

persicaria tinctoria, blue gold

We're excited to collaborate with PICA on this project as well as to see what growing indigo, and creating our own natural dyes, is all about. We hope interest in traditional natural dyes continue to grow, as the World Bank estimates the commercial dyeing of fabrics to contribute up to 20% of world wide industrial water pollution. Dozens of chemicals are making their way into the water supply, many of which can't be removed.